1. Field of the Invention
The invention herein pertains to the field of herbicides. In particular, the invention pertains to a synergistic herbicidal composition having as the active ingredient a mixture of N-(butoxymethyl)-6'-tert-butyl-2-chloro-o-acetotoluidide and N-(3-chloro-4-methyl phenyl)-N',N'-dimethylurea (chlortoluron). The herbicidal composition herein has particular application in the control of undesired plants associated with cereal crops, e.g., wheat and barley.
2. Description of the Prior Art
It is known in the prior art to use various N-halo-substituted- and/or alkyl-substituted phenyl-N',N'-dialiphatic ureas (sometimes referred to as "trisubstituted ureas") as herbicides, either individually or in combination with various other herbicidal compounds. In such urea compounds, the aliphatic substituents are commonly alkyl, alkenyl, alkoxy groups, but other groups may also be used.
A wide variety of chemical compounds have been admixed with various members of the above-mentioned class of trisubstituted ureas in efforts to discover new herbicidal compositions having unique additive, antagonistic or synergistic properties with respect to different weed plants associated with various crop plants. Illustrative of prior art herbicide mixtures containing trisubstituted ureas and other compounds are those containing a trichlorophenylacetic acid, its salts, amides or esters (U.S. Pat. No. 3,163,516); alkyl- and/or halo-substituted phenoxy-acetic acid, -salt, -amide or -ester (U.S. Pat. No. 2,709,648); trichlorobenzoic acid or its salts (U.S. Pat. No. 3,253,903); halo- and nitro-substituted diphenyl ethers (U.S. Pat. No. 3,484,230); triazines (U.S. Pat. No. 3,022,150); CF.sub.3 /NO.sub.2 -substituted toluidine (U.S. Pat. No. 3,373,010) and thiolcarbamic acid esters (U.S. Pat. No. 3,095,299).
In further particular, U.S. Pat. No. 2,655,445 discloses a generic class of herbicidal trisubstituted ureas which encompasses chlorotoluron, but this compound is not specifically mentioned. On the other hand, chlorotoluron or analogs or isomers thereof, are specifically-named herbicidal compounds which may be used alone or in conjunction with other named herbicidal compounds, (none of which are acetanilides) in British Pat. Nos. 1,253,143, 1,255,258 and 1,260,460. Herbicidal compositions of chlorotoluron are available, e.g., as Dicurane 80 WP.
It is also known in the prior art to use various 2-halo-2',6'-dialkyl-N-(alkoxyalkyl) acetanilides as herbicides either individually or in combination with other herbicidal componds. For example, U.S. Pat. No. 3,551,132 discloses the herbicidal use of 2-chloro-2',6'-diethyl-N-(methoxymethyl)acetanilide (common name alachlor) admixed with 3'-(carbamoyloxy) anilides. British Pat. No. 1,176,547 discloses the herbicidal use of a mixture of alachlor and linuron, i.e., 3-(3,4-dichlorophenyl)-1-methoxy-1-methylurea.
In still further particular, U.S. Pat. Nos. 3,442,945 and 3,547,.620 both of which are also assigned to applicant's assignee, disclose a broad class of herbicidal 2-halo-2',6'-dialkyl-N-(alkoxyalkyl) acetanilides, expressly including N-(butoxymethyl)-6'-tert-butyl-2-chloro-o-acetotoluidide (the nomenclature in said patents follows the acetanilide nomenclature rather than the toluidide nomenclature). This compound has tentatively been designated as "terbuchlor"; application is being made by applicant's assignee to the American Standards Institute for registration of this name as the common name for said compound. Hence, the term "terbuchlor" will sometimes be used hereafter in the specification for brevity. The U.S. Pat. Nos. 3,442,945 and 3,547,620 both disclose that the acetanilide compounds therein may be admixed with other herbicidal compounds, including certain trisubstituted ureas, such as linuron, monuron or diuron.
Therefore, as pertains to the invention herein, it appears that the closest prior art would be those patents which describe the herbicidal use of the specific components herein, i.e., British Pat. Nos. 1,253,143, 1,255,258 and 1,260,460 for disclosures of herbicides containing chlorotoluron or its isomers or analogs; British Pat. No. 1,176,547 for its disclosure of herbicidal mixtures of alachlor and linuron, and U.S. Pat. Nos. 3,442,945 and 3,547,620 for their disclosures of terbuchlor-containing compositions which may include linuron, monuron or diuron.
Absent from the prior art, to applicant's knowledge, is any recognition or disclosure of a herbicidal composition comprising chlorotoluron and terbuchlor which together impart complementary, supplementary and/or synergistic action with respect, particularly, to undesirable vegetation associated with cereal crops, such as wheat and barley.
The phenomenon of synergism is well known to those skilled in the art and, in the herbicidal art, relates to herbicidal compositions of mixed components whose total herbicidal effect is unexpectedly greater than the additive effect of the individual components on particular plants or a spectrum of plants. The use of synergistic mixtures for the control of plant growth permits the utilization of a lesser total amount of herbicidal composition and/or lesser quantities of individual components in the composition to obtain the same or improved results than are obtained when a greater amount of herbicidal composition containing only the individual components or additive mixtures thereof. The use of lesser quantities of active ingredients in a herbicidal composition may also increase the margin of crop safety in the use of those active ingredients.
The concepts of synergism and antagonism (i.e., negative, neutralizing or nullifying effect of one component on another component) in herbicidal combinations have been reduced to mathematical formulation and graphical representation by some authors. For example, by the method described by S. R. Colby in "Weeds", Vol. 15, No. 1 (1967) pages 20-22, the expected response of a combination of herbicides is obtained by taking the product of the percent-of-control values for the individual herbicides and dividing by (100).sup.n.sup.-1 where n is the number of herbicides in the combination.
Another method of expressing synergism and antagonism is described by P. M. L. Tammes in "Netherlands Journal of Plant Pathology", 70 (1964), 73-80. By the Tammes method, a graphic representation is given of the effect of mixtures of herbicides. Each of the components is expressed as a coordinate on a graph and quantiatively defined effect, e.g., a percent plant mortality, e.g., 50%, 85%, etc., is inserted in the graph. These values are obtained by interpolation. The line which connects the points is called an "isobole". With an isobole the effect of different proportions of the individual components can be evaluated. The Tammes isoboles method has proven reliable in evaluating the synergistic effect of the herbicidal composition of this invention.
As used herein the term "active ingredient" denotes a mixture of terbuchlor and chlorotoluron having the combined supplementary, complementary and synergistic properties unique to this mixture.
The term "plant" as used herein encompasses dormant seeds, germinant seeds, germinative seeds, emerging seedlings and established vegetation including roots and above-ground portions.
The term "control" as used herein is inclusive of the effects of killing, inhibiting the growth, reproduction or proliferation and removing, destroying or otherwise diminishing the occurrence or activity of plants and is applicable to any of the stated effects or combinations thereof.